MgF2 Retarders: Low Order

The retarders are single plates with a thickness of 0.15 mm to 0.5 mm. The general properties and the working principle are identical with those of the low order retarders made of quartz crystal. The main difference is the broader spectral transmission of MgF2 which reaches from approx. 120 nm to 7 µm. In some cases the lack of optical activity in MgF2 is of advantage, as its presence in quartz crystal may be disturbing in applications where an extremely high degree of polarisation is of concern.
The wavefront distortion is λ/10 (at λ = 550 nm) and the wedge error is smaller than 2’’. The accuracy of the path difference is ± 3 nm.
The useable spectral width for a single plate in the visible and ultraviolet spectral range is similar to that of quartz low order plates. For wavelengths above 3.5 µm single plates can be manufactured with an order number of zero. In this case the estimation of the spectral width is identical as in the case of two part zero order plates.
The deviation ΔR of the path difference from the nominal value R (both in nm) due to a temperature change by ΔT (in K) or due to tilt by Δφ (in degrees) can be estimated as follows:

ΔR≈-(0,1 nm/K)•ΔT
ΔR≈±(0,2 nm/Grad²)•Δφ²

The deviations will be smaller than the production tolerance for temperature changes up to ±30 K or for a tilt up to ±4°.
The plates are delivered without AR coating mounted in a cylindrical holder made of anodized aluminum and engraved with the direction of the fast axis, the path difference and the design wavelength.

Important note

Please specify required wavelength when ordering.
The prices apply to standard wavelengths according to the following table:

Available on special order

• non-standard wavelengths have a surcharge:
  clear aperture 9.5 mm and 14.5 mm → RLM 0.1
  clear aperture 19.5 mm and 24.5 mm → RLM 0.2
• Antireflection coating → on request
• other dimensions → on request